Facebook found itself in hot water several weeks ago after a report from Gizmodo alleged that Facebook’s news-curation team kept conservative news topics and stories out of Facebook’s prominent trending-news section. Former employees told Gizmodo that even if right-wing topics or news sources were trending, they were often suppressed. Facebook’s V.P. of search, Tom Stocky, responded with a statement denying virtually all of the Gizmodo report, saying Facebook “found no evidence that the anonymous allegations are true.” Then came a subsequent report from The Guardian, which seemed to contradict Facebook’s statement and confirm parts of Gizmodo’s: according to leaked documents obtained by the outlet, Facebook’s trending-topics team gave editors the privilege of injecting or removing topics from the trending-news bar, at their discretion—something Facebook denied. Facebook sources also provided the paper with a list of 1,000 trusted news sources that its editors use as a reference for trending news, and conservative outlets like Breitbart and Redstate are among them.

The notably unproductive U.S. Senate Commerce Committee decided to pounce, sending a public letter to Facebook C.E.O. Mark Zuckerberg, looking for answers to questions regarding Facebook’s trending-news practices. Now, Facebook has issued a more thorough response to these reports, as well as the Senate Republicans’ letter.

In its response to Chairman John Thune, the company says its own internal investigation “has revealed no evidence of systematic political bias in the selection or prominence of stories included in the Trending Topics feature,” Facebook’s general counsel Colin Stretch wrote. However, Facebook will still be changing some of its own internal guidelines for choosing stories for the trending-news bar, and no longer relying on that list of appropriate Web sites to determine the importance of a news topic that its algorithm finds. “Our investigation could not fully exclude the possibility of isolated improper actions or unintentional bias in the implementation of our guidelines or policies,” Stretch said. Facebook’s news editors will be retrained as well.